Use tryBindIfNeeded(), send player started only if player!=null

This commit fixes one way ghost notifications could be produced (although I don't know if there are other ways). This is the call chain that would lead to ghost notifications being created:
1. the system starts `PlayerService` to query information from it, without providing `SHOULD_START_FOREGROUND_EXTRA=true`, so NewPipe does not start the player nor show any notification, as expected
2. the `PlayerHolder::serviceConnection.onServiceConnected()` gets called by the system to inform `PlayerHolder` that the player started
3. `PlayerHolder`  notifies `MainActivity` that the player has started (although in fact only the service has started), by sending a `ACTION_PLAYER_STARTED` broadcast
4. `MainActivity` receives the `ACTION_PLAYER_STARTED` broadcast and brings up the mini-player, but then also tries to make `PlayerHolder` bind to `PlayerService` just in case it was not bound yet, but does so using `PlayerHolder::startService()` instead of the more passive `PlayerHolder::tryBindIfNeeded()`
5. `PlayerHolder::startService()` sends an intent to the `PlayerService` again, this time with `startForegroundService` and with `SHOULD_START_FOREGROUND_EXTRA=true`
6. the `PlayerService` receives the intent and due to `SHOULD_START_FOREGROUND_EXTRA=true` decides to start up the player and show a dummy notification

Steps 3 and 4 are wrong, and this commit fixes them:
3. `PlayerHolder` will now broadcast `ACTION_PLAYER_STARTED` when the service connects, only if the player is not-null
4. `PlayerHolder::tryBindIfNeeded()` is now used to passively try to bind, instead of `PlayerHolder::startService()`

Author: Stypox

app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java

@@ -1416,10 +1416,8 @@ public void onReceive(final Context context, final Intent intent) {
                             bottomSheetBehavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
                         }
                         // Rebound to the service if it was closed via notification or mini player
-                        if (!playerHolder.isBound()) {
-                            playerHolder.startService(
-                                    false, VideoDetailFragment.this);
-                        }
+                        playerHolder.setListener(VideoDetailFragment.this);
+                        playerHolder.tryBindIfNeeded(context);
                         break;
                 }
             }

app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java

@@ -192,9 +192,11 @@ public void onServiceConnected(final ComponentName compName, final IBinder servi
             startPlayerListener();
             // ^ will call listener.onPlayerConnected() down the line if there is an active player
 
-            // notify the main activity that binding the service has completed, so that it can
-            // open the bottom mini-player
-            NavigationHelper.sendPlayerStartedEvent(localBinder.getService());
+            if (playerService != null && playerService.getPlayer() != null) {
+                // notify the main activity that binding the service has completed and that there is
+                // a player, so that it can open the bottom mini-player
+                NavigationHelper.sendPlayerStartedEvent(localBinder.getService());
+            }
         }
     }